1. Field of the Invention
The invention relates to the field of automotive interlocks.
2. Prior Art
It is known to secure a motor vehicle against operation by a person who has consumed alcohol. A typical arrangement, known as an breath alcohol ignition interlock device (BAIID), involves a relay between the breath tester and the starter motor, pursuant to which the starter motor cannot be engaged until a satisfactory breath sample has been given. In this regard, a ‘satisfactory’ gas sample is conventionally understood to be one that (i) is of sufficient volume and pressure to permit alcohol analysis; (ii) has alcohol concentration below a predetermined limit; and (iii) appears to have originated from the exhaled breath of a human being. Criterion (iii) is often assessed through measurements of pressure, humidity and temperature, but various other techniques such as hum recognition sensors are occasionally used. In some jurisdictions, a person convicted of driving under the influence of alcohol may be required by law to have a device of this type installed as a condition associated with the extension of driving privileges. While the engine is running, the BAIID may randomly require the driver to provide another breath sample. The time between required breath samples is dependent on the setting of the unit but, for example, it is typical for random breath samples to be required every 10 to 20 minutes while the vehicle is in operation. All events are logged, for the purpose of, inter alia, compliance purposes. It is known for persons to attempt to circumvent a BAIID device by having a “sober” friend blow into the device to start or maintain operation of the vehicle.
Other difficulties with existing systems may be appreciated in view of the description below.